Patent GB-617962-A (GB)
Title: Improvements in or relating to metal meshes
IPC: H01J29/41
Filed: 1945-09-08
Abstract: 617,962. Making metal mesh screens and dies. McGEE, J. D., and HOLMAN, H. E. Sept. 8, 1945, Nos. 23180/45 and 1313/46. [Classes 83 (ii) and 83 (iv)] [Also in Groups V, XXXVI and XL (a)] Jointing; forging-dies; powder metallurgy.-The filaments of a metal mesh, particularly one to form part of a doublesided mosaic screen in a television transmitting tube, are of maximum width in the mid-plane of the mesh and decrease in width to each outer surface, e.g. are of diamond-shaped crosssection, and the parts of the filaments on opposite sides of the mid-plane of the mesh are formed in separate grooved matrices or at different times in a single grooved matrix. In one form, Figs. 1-4 (not shown), a mesh formed by the method described in Specification 598,994 is placed between two matrices having grooves of triangular cross-section and pressed into the desired shape. The matrices may be of copper faced with chromium, and may be aligned by any of the methods described in Specification 598,994; a potential difference may be applied between the mesh and one matrix to hold them together until the other matrix is closed upon them, either the mesh or the former matrix being coated with insulating material such as a lacquer or oxide. After pressing, the separation of the matrices is facilitated by making the grooves in one matrix more acute in angle than those in the other matrix, so that the mesh is retained in the former matrix. This matrix is then removed from the mesh by dissolving it in acid. Alternatively, the mesh may be sprayed with lacquer, e.g. a solution of resin in alcohol with a plasticizer, before pressing, which bonds the mesh to the matric in which it is first inserted. The mesh comprises two sets of intersecting filaments, and the interstices may be filled with mosaic elements. In another form, Fig. 5, two meshes 9, 10 whose filaments have a triangular crosssection are formed in separate matrices or at different times in a single matrix, and may be formed by compressing metal powder or metal foil, or by electrodeposition. The aluminium meshes are then insulated by anodising, the flat surfaces 12 are coated with lead borate which is melted to form a glaze at 600‹ C., the meshes are aligned and pressed together, heated to the melting point of lead borate and allowed to cool. In another form, Fig. 7, a positive matrix 15 is made by electroposition on a master impression obtained by electrodeposition on a wax plate ruled with two sets of intersecting grooves, and a negative matrix 18 is made by electrodeposition on the positive matrix 15. Aluminium powder 28 is then placed in the grooved matrices, and the latter aligned by pins and pressed together to render the powder into a coherent mesh. Excess metal is removed from the formed mesh by etching or by forcing powder through the interstices of the mesh. Metal foil can be used instead of powder. A similar method may be used to form the meshes of Fig. 5, each triangular mesh being formed by separately loading two matrices with metal powder and compressing each lot of powder or foil with the aid of a flat plate, Fig. 14 (not shown). The meshes are then secured together as described with reference to Fig. 5 or by pressing the meshes together until the opposed surfaces become coherent. The powder may be replaced by metal foil. A thin layer of metal powder or a thin metal foil placed between the meshes improves the bonding. After pressing, the copper matrices are removed by dissolving in nitric acid and any excess of the thin metal layer is removed by etching, e.g. aluminium may be etched in sodium hydroxide or hydrochloric acid. In another form, Fig. 12, a deformable matrix 30 backed by a layer of rubber, pulp board, or bristol board co-operates with a rigid matrix 33 to form a mesh 29, and the matrices are then dissolved away. The mosaic elements may be produced as described in Specifications 590,928, 593,107 and 595,825, [all in Group XL]. Alternatively, an insulated mesh is surrounded by finely divided silver and the silver compressed between two flat metal plates so as to form a metal biscuit enclosing the mesh. The excess of the pressed metal is removed by lapping. In a modified process, the flat plates may be faced with rubber and a small quantity of silver applied between them and compressed, further small amounts of silver being added and compressed successively until the interstices of the mesh are filled. In the processes in which metal foil or powder is placed between two matrices, the loaded matrices may be heated to a sintering temperature and the mesh rendered coherent without using high pressures. The meshes in all cases may be of aluminium, gold, silver or platinum, and may be of two sets of intersecting filaments or of a single set of non-intersecting parallel filaments.